Chamber top view · drawn to one scale (ticks in mm) · playback slowed
drawn paths (click one):
Collected current
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Proton beam energy at the collector
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Selected path
Blue dots: the RF phase (degrees from the crest) at which the ion crossed the gap, one dot per crossing — 0° is the crest, positive is late. Yellow line: its energy (keV) after each crossing. A phase that drifts away from 0° is the ion falling out of step with the RF.
Off resonance, each gap crossing arrives earlier or later than the crest, so the push gets weaker each turn. more
An ion gains energy only while it crosses the gap near the crest of the RF wave. If the RF frequency does not match the ion's orbit frequency, each successive crossing arrives a little earlier or later on the wave, so the push shrinks, then reverses: the ion stops gaining and spirals no further. The phase per crossing in this panel shows that drift directly.